
MOTOROLA
Chapter 9. External Bus Interface
9-19
Bus Operations
slave is burstable, it negates the burst-inhibit (BI) signal. If the slave cannot burst, it asserts
During the data phase of a burst-write cycle, the master drives the data. It also asserts BDIP
if it intends to drive the data beat following the current data beat. When the slave has
received the data, it asserts TA to indicate to the master that it is ready for the next data
transfer. The master again drives the next data and asserts or negates the BDIP signal. If the
master does not intend to drive another data beat following the current one, it negates BDIP
to indicate to the slave that the next data beat transfer is the last data of the burst-write
transfer.
timing mode, assertion of BDIP is delayed by the number of wait states in the first data beat.
This implies that for zero-wait-state cycles, BDIP assertion time is identical in normal and
late modes. Cycles with late BDIP generation can occur only during cycles for which the
more information.
In the MPC565/MPC566, no internal master initiates write bursts. The MPC565/MPC566
is designed to perform this kind of transaction in order to support an external master that is
During the data phase of a burst-read cycle, the master receives data from the addressed
slave. If the master needs more than one data beat, it asserts BDIP. Upon receiving the
second-to-last data beat, the master negates BDIP. The slave stops driving new data after it
receives the negation of the BDIP signal at the rising edge of the clock.
Burst inputs (reads) in the MPC565/MPC566 are used only for instruction cycles. Data load
cycles are not supported.
Figures
9-12 through
9-21 are examples of various burst cycles, including illustrations of
burst-read and burst-write cycles for both the 16- and 32-bit port sizes.